Randomly place and scale objects?
The best tool for this situation is the randomize transform tool. It's not a tool that has a shortcut key and it's buried in the object menu (Object &gt; Transform &gt; Randomize Transform), so the easiest way to access it is to simply search it using Space.
To create the wall from that image, do the following:

Create a plane for the wall.

Duplicate a few cubes around

Use the randomize transform tool and set it to affect the location of the objects (except the axis along the wall) and the scale of the object. Something like this:


You'll get something like this: